Retroreflective scan module for electro-optical readers

ABSTRACT

An electro-optical, retroreflective scanning module has a base, a first circuit board, and a second circuit board mounted orthogonal to the first circuit board. The base supports a light emitter for producing a scanning beam. The beam reflects off a generally planar scan mirror affixed to a stationary concave collection mirror, to a reflector mounted on a drive for oscillation. A detector included in the module senses light reflected from an indicia scanned by the beam. The reflected light is reflected off the reflector and directed to the collection mirror before reaching the detector. The beam and the field of view of the detector are simultaneously scanned.

RELATED APPLICATIONS

This application is a division of U.S. Ser. No. 08/727,944, filed Oct.9, 1996, abandoned, and claims the benefit of U.S. Provisionalapplication Serial No. 60/005,949, filed Oct. 10, 1995.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to electro-optical readers or scanning systems,such as bar code symbol scanners, and more particularly toretroreflective laser scanning modules for use in applications requiringparticularly compact scanners.

2. Description of the Related Art

Electro-optical readers, such as bar code symbol readers, are now quitecommon. Typically, a bar code symbol comprises one or more rows of lightand dark regions, typically in the form of rectangles. The widths of thedark regions, i.e., the bars, and/or the widths of the light regions,i.e., the spaces, between the bars indicate encoded information to beread.

A bar code symbol reader illuminates the symbol and senses lightreflected from the coded regions to detect the widths and spacings ofthe coded regions and derive the encoded information. Bar code readingtype data input systems improve the efficiency and accuracy of datainput for a wide variety of applications. The ease of data input in suchsystems facilitates more frequent and detailed data input, for exampleto provide efficient inventories, tracking of work in progress, etc. Toachieve these advantages, however, users or employees must be willing toconsistently use the readers. The readers therefore must be easy andconvenient to operate.

A variety of scanning systems are known. One particularly advantageoustype of reader is an optical scanner which scans a beam of light, suchas a laser beam, across the symbols. Laser scanner systems andcomponents of the type exemplified by U.S. Pat. Nos. 4,387,297 and4,760,248—which are owned by the assignee of the instant invention andare incorporated by reference herein—have generally been designed toread indicia having parts of different light reflectivity, i.e., barcode symbols, particularly of the Universal Product Code (UPC) type, ata certain working range or reading distance from a hand-held orstationary scanner.

FIG. 1a illustrates an example of a prior art bar code symbol reader 10implemented as a gun shaped device, having a pistol-grip type of handle53. A lightweight plastic housing 55 contains a light source 46, adetector 58, optics 57, signal processing circuitry 63, a programmedmicroprocessor 40, and a power source or battery 62. Alight-transmissive window 56 at the front end of the housing 55 allowsan outgoing light beam 51 to exit and an incoming reflected light 52 toenter. A user aims the reader 10 at a bar code symbol 70 from a positionin which the reader 10 is spaced from the symbol, i.e. not touching thesymbol or moving across the symbol.

As further depicted in FIG. 1a, the optics may include a suitable lens57 (or multiple lens system) to focus the scanned beam into a scanningspot at an appropriate reference plane. The light source 46, such as asemiconductor laser diode, introduces a light beam into an optical axisof the lens 57, and the beam passes through a partially-silvered mirror47 and other lenses or beam shaping structures as needed. The beam isreflected from an oscillating mirror 59 which is coupled to a scanningdrive motor 60 energized when a trigger 54 is manually pulled. Theoscillation of the mirror 59 causes the outgoing beam 51 to scan backand forth in a desired pattern.

A variety of mirror and motor configurations can be used to move thebeam in a desired scanning pattern. For example, U.S. Pat. No. 4,251,798discloses a rotating polygon having a planar mirror at each side, eachmirror tracing a scan line across the symbol. U.S. Pat. Nos. 4,387,297and 4,409,470 both employ a planar mirror which is repetitively andreciprocally driven in alternate circumferential directions about adrive shaft on which the mirror is mounted. U.S. Pat. No. 4,816,660discloses a multi-mirror construction composed of a generally concavemirror portion and a generally planar mirror portion. The multi-mirrorconstruction is repetitively reciprocally driven in alternativecircumferential directions about a drive shaft on which the multi-mirrorconstruction is mounted.

The light 52 reflected back by the symbol 70 passes back through thewindow 56 for transmission to the detector 58. In the exemplary reader10 shown in FIG. 1a, the reflected light reflects off of mirror 59 andpartially-silvered mirror 47 and impinges on the light sensitivedetector 58. The detector 58 produces an analog signal proportional tothe intensity of the reflected light 52.

The signal processing circuitry includes a digitizer 63 mounted on aprinted circuit board 61. The digitizer processes the analog signal fromdetector 58 to produce a pulse signal where the widths and spacingsbetween the pulses correspond to the widths of the bars and the spacingsbetween the bars. The digitizer serves as an edge detector or waveshaper circuit, and a threshold value set by the digitizer determineswhat points of the analog signal represent bar edges. The pulse signalfrom the digitizer 63 is applied to a decoder, typically incorporated inthe programmed microprocessor 40 which will also have associated programmemory and random access data memory. The microprocessor decoder 40first determines the pulse widths and spacings of the signal from thedigitizer. The decoder then analyses the widths and spacings to find anddecode a legitimate bar code message. This includes analysis torecognize legitimate characters and sequences, as defined by theappropriate code standard. This may also include an initial recognitionof the particular standard to which the scanned symbol conforms. Thisrecognition of the standard is typically referred to asautodiscrimination.

To scan the symbol 70, the user aims the bar code reader 10 and operatesmovable trigger switch 54 to activate the light source 46, the scanningmotor 60 and the signal processing circuitry. If the scanning light beam51 is visible, the operator can see a scan pattern on the surface onwhich the symbol appears and adjust aiming of the reader 10 accordingly.If the light beam 51 produced by the source 46 is marginally visible, anaiming light may be included. The aiming light, if needed, produces avisible-light spot which may be fixed, or scanned just like the laserbeam 51. The user employs this visible light to aim the reader at thesymbol before pulling the trigger.

The reader 10 may also function as a portable data collection terminal.If so, the reader 10 would include a keyboard 48 and a display 49, suchas described in the previously noted U.S. Pat. No. 4,409,470.

In electro-optical scanners of the type discussed above, the “scanengine” including the laser source, the optics the mirror structure, thedrive to oscillate the mirror structure, the photodetector, and theassociated signal processing and decoding circuitry all add size andweight to the scanner. In applications involving protracted use, a largeheavy hand-held scanner can produce user fatigue. When use of thescanner produces fatigue or is in some other way inconvenient, the useris reluctant to operate the scanner. Any reluctance to consistently usethe scanner defeats the data gathering purposes for which such bar codesystems are intended. Also, a need exists for compact scanners to fitinto small compact devices, such as notebooks.

Thus an ongoing objective of bar code reader development is tominiaturize the reader as much as possible, and a need still exists tofurther reduce the size and weight of the scan engine and to provide aparticularly convenient to use scanner. The mass of the movingcomponents should be as low as possible to minimize the power requiredto produce the scanning movement.

It is also desirable to modularize the scan engine so that a particularmodule can be used in a variety of different scanners. A need exists,however, to develop a particularly compact, lightweight module whichcontains all the necessary scanner components.

Smaller size scanning components tend to operate at higher scanningfrequencies. In typical bar code scanning applications, however, thescanning frequency of the moving beam spot should be relatively low,typically 20 Hz or less. If the frequency increases, the speed of thespot as it passes over the symbol increases. The signals produced by thedetector also increase in frequency, and consequently the bandwidth ofthe processing circuitry for analysing the detector signals must beincreased. Also, operation at higher scanning frequencies generallyproduces detector signals which include higher levels of noise, makingaccurate decoding more difficult.

SUMMARY OF THE INVENTION Objects of the Invention

The objective of this invention is to develop an entirelyself-contained, electro-optical, retroreflective scanning module,including all components necessary to generate the light beam, scan thebeam in a pattern across a symbol, detect light reflected back by thesymbol and process signals representative of the reflected light. Inthis regard, the retroreflective module should be small, lightweight andeasy to incorporate into a variety of different types of electro-opticalscanning systems.

Another objective of this invention is to minimize the size and weightof the components used to produce the scanning motion of the light beam,and to collect the reflected light.

Another related objective is to develop an electro-optical scanningsystem which is smaller and lighter in weight, when held by an operator,and which it is easier to manipulate to scan encoded indicia, ascompared to known system.

Features of the Invention

In keeping with these objects, one feature of this invention is embodiedin a self-contained, electro-optical, retroreflective scanning modulefor reading optically encoded indicia having parts of different lightreflectivity. The module includes a base; a light source on the base,for emitting a light beam along an outgoing path toward the indicia forreflection therefrom; a light detector on the base, for detecting lightreflected from the indicia along an incoming path over a field of view,and for generating electrical signals corresponding to the indicia partsof different light reflectivity; a movable reflector mounted in thepaths of the light beam and the reflected light; and a drive on thebase, for moving the movable reflector to sweep the light beam acrossthe indicia, and to simultaneously sweep the field of view.

In accordance with this invention, the light source is mounted in acasing, and a stationary collecting mirror is fixedly mounted on thecasing, and a stationary scan mirror is fixedly mounted on thecollecting mirror. Advantageously, the collecting mirror is concavelycurved, and the scan mirror is planar. Also, a bracket holds the mirrorsat a distance from the casing.

Another advantageous aspect of this invention is embodied in fixedlymounting the casing and the mirrors at one of two end regions of thebase, and in mounting the movable reflector for movement at the other ofthe end regions of the base. The light detector is mounted at a centralregion of the base and faces the collecting mirror, and is located atthe centre of curvature thereof.

The drive includes an elongated support having opposite end portions.The reflector is mounted at one of the end portions of the support. Thedrive includes a permanent magnet mounted at the other of the endportions of the support, and an electromagnetic coil mounted inproximity to the permanent magnet and operative, when an alternatingdrive signal is applied to the coil, for producing an alternatingmagnetic field which acts on the permanent magnet to oscillate themagnet and, in turn, the support and the reflector mounted thereon aboutan axis located approximately midway between the reflector and thepermanent magnet.

The resulting compact construction enables the retroreflective module tobe placed within a variety of system configurations, especiallyminiature ones.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings.Further features of the invention are set out in the appendedindependent claims, and further preferred features are set out in thedependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a is a schematic view of a prior art hand-held laser scanner anddata collection terminal;

FIG. 1b is a schematic view of a hand-held gun-type scanner according tothe present invention;

FIG. 2 is a perspective view of one embodiment of a scanning module inaccordance with the invention, with certain parts broken away forclarity;

FIG. 3 is a top plan view of the module of FIG. 2, again with certainparts removed to show the interior of the module;

FIG. 4 is a left side elevational view of the module of FIG. 2;

FIG. 5 is a right side elevational view of the module of FIG. 2;

FIG. 6 is an elevational view of a drive component of the module of FIG.2;

FIG. 7a is a perspective view of another embodiment of a scanning modulein accordance with this invention;

FIG. 7b is a plan view of another embodiment of a scanning module inaccordance with this invention;

FIG. 8 shows a scanner module according to another aspect of theinvention;

FIG. 9 shows a scanner module according to yet a further embodiment ofthe invention;

FIG. 10 shows an alternative embodiment of the scanner module shown inFIG. 9;

FIG. 11 shows a nominal bar code symbol and reading beam spot;

FIG. 12 shows a laser focusing aperture and a beam waist;

FIG. 13a shows an improved aperture shape;

FIG. 13b shows an alternative aperture shape to that of FIG. 13a;

FIG. 13c shows an alternative aperture shape to that of FIG. 13a;

FIG. 14 shows a nominal MTF curve based on aperture shape for a 6 mildensity code;

FIG. 15 shows an MTF curve for an aperture shape for a 7.5 mil densitybar code;

FIG. 16 shows an MTF curve for a 20 mil density bar code;

FIG. 17 shows an MTF curve for a 55 mil density bar code;

FIG. 18 shows a schematic interconnection between a scanning module anda decoder module;

FIG. 19 shows a conventional two photodiode detector system from above;

FIG. 20 shows the system of FIG. 19 from one side;

FIG. 21 shows the system of FIG. 19 from the front;

FIG. 22 shows an improved detector system according to the presentinvention from above;

FIG. 23 shows the system of FIG. 22 from one side;

FIG. 24 shows the system of FIG. 22 from the front;

FIG. 25 shows a portion of a conventional scanning module;

FIG. 26 shows a decoder module according to another aspect of thepresent invention; and

FIG. 27 shows a “back to back” dual laser arrangement according toanother aspect of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As used in this specification and in the appended claims, the term“indicia” broadly encompasses not only symbol patterns composed ofalternating bars and spaces of various widths commonly referred to asbar code symbols, but also another one or two dimensional graphicpatterns, as well as alphanumeric characters. In general, the term“indicia” may be recognized of pattern or information which may berecognized or identified by scanning a light beam and detectingreflected or scattered light as a representation of variations in lightreflectivity at various points of the pattern or information. A bar codesymbol is one example of an “indicia” which the present invention canscan.

FIGS. 2 to 6 show the construction of a small sized, self-contained,retroreflective scanning module 400. The module 400 is substantiallyrectangular and in one example was made as small as 1.35″×0.95″×0.69″. Aperspective view of the module 400, with certain portions removed, isshown in FIG. 2.

Whilst the scanning module is discussed hereafter with reference to agun-type scanner it will be appreciated that it would also be suitableto incorporate the module in any appropriate system for example ascanner terminal including a scanner portion and a key pad and/ordisplay screen.

The module includes a generally planar, elongated, metal base 410,typically formed of aluminum. Base 410 has one end region 402, anopposite end region 404, and an intermediate or central region 406. Asemi-cylindrical casing or housing 412 contains a laser diode and afocusing module similar to those shown in U.S. Pat. No. 5,367,151 ownedby the assignee of the instant application, and whose disclosure isincorporated herein by reference hereto.

As shown, the casing 412 is bolted at bolt 408 to, but could also beintegrally formed as a section of, the base 410. The casing 412 and thecase 410 serve as a heat sink to dissipate heat generated by the laserdiode during scanning operations.

The module 400 includes two circuit boards positioned at right angles toeach other. A first circuit board 416, mounted orthogonal to the base410 at one end thereof, supports part of the circuitry used by thescanner. Typically, the first circuit board 416 supports the circuitryfor producing the current to drive the laser diode.

A second circuit board 418 is mounted orthogonal to the first circuitboard and parallel to the base 410. Assuming that the flat major surfaceof the base 410 is the bottom of the module 400, the second circuitboard 418 would form the top of the module 400. A flexible electriccable (not illustrated) connects the circuitry on the first and secondcircuit boards together. The second circuit board 418 supports theremainder of the necessary circuitry. Of particular note, the board 418supports an application specific integrated circuit 419 which includesthe analog signal processing circuitry, the digitizer and may includethe microprocessor-based decoder.

FIG. 3 is a top view of the module 400, taken as if the second circuitboard 418 were omitted, to provide an illustration of the interior ofthe module. As shown, a support structure 300 provides flexible supportfor a reflector 359 so as to permit reciprocal motion of the reflector.The flexible support structure is described below in connection withFIG. 6.

The interior of the module also contains a stationary mirrored structure200 fixed to the casing 412 by a bracket 202 at end region 402 of thebase. The mirrored structure 200 includes a concavely curved collectionmirror 204 having a centre of curvature at which a photodetector 206 islocated. The photodetector 206 is mounted at the central region 406 ofthe base 410 within a housing 208. A filter 210 is located upstream ofthe photodetector 206 within the housing 208.

A louvre of a known type can be placed in front of the photodetector 206although this is not shown in the drawings.

A generally planar scan mirror 212 is fixedly mounted on the collectionmirror 204, and preferably is integrally formed and molded as one-piecetherewith. The scan mirror 212 is inclined and faces both the laserdiode within the casing 412, as well as the reflector 359. The frontsurfaces of the mirrors 204, 212 are provided with a light-reflectivecoating.

As shown in FIG. 6, the support structure 300 includes a U-shaped member303 having a first arm 305 to which the reflector 359 is attached. Asecond arm 307 of the member 303 supports a permanent magnet 309. Astraight section 311 extends between and connects the first and secondarms together to form the U-shape of member 303.

A pair of flexible strips 321,323 connects to one of the arms of theU-shaped member 303 and serves as a planar spring. These spring stripscomprise a flat sheet of flexible plastic material such as Mylar™ orKapton™ film, or other flexible elements such as a flat strip ofnon-magnetic metal like a beryllium-copper alloy. In the illustratedrest position, the strips 321,323 remain in a relatively unflexed stateand extend in a direction substantially parallel to the straight section311 in the space between the first arm 303 and the second arm 307. Oneset of ends of the strips 321,323 connects to the first arm 305, and theopposite set of ends of the strips 321,323 is fixed.

More specifically, the ends of the Mylar™ or Kapton™ material sheetsforming the flexible strips 321,323 are fastened by suitable fasteners325 and thereby clamped between a plate 327 and a frame member 326extending from the rear surface of first arm 305 and a portion of thelower surface of the straight section 311. The opposite ends of thestrips 321,323 are fastened to a fixed support by suitable fasteners 329which clamp the strips between a plate 331 and an enlarged portion of astationary arm 337 extending out from a support pedestal 335 (FIG. 2).The support pedestal 335 is mounted on the flat section of the metalbase 410 at the end region 404.

The components of the support structure 300, the reflector 359 and themagnet 309 are dimensioned such that the weight of the magnet balancesthe weight of the reflector with respect to a pivot axis A approximatelyhalf way between the reflector and the magnet. As a result, the strips321,323 function as planar leaf spring elements and flex about thatpivotal axis. The pivot axis A extends perpendicular to the flat lowerportion of the base 410 (or vertical in FIG. 6).

An electromagnetic coil 333 is attached to the lower surface of thesecond circuit board 418 by a bracket 334 (FIG. 5). Mounting of thesecond circuit board 418 on the top of the module 400 positions theattached coil 333 in close proximity to the permanent magnet 309, asshown in FIG. 3. The axis between the north and south poles of thepermanent magnet 309 is aligned in the plane of the drawing of FIG. 3,i.e. parallel to the flat lower portion of the base 410. When analternating current is introduced through the coil of the electromagnet333, interaction between magnetic fields of the coil and the permanentmagnet 309 produce an oscillatory movement of the permanent magnet 309and a rotational oscillation of the attached member 303 against thereturn forces produced by the flat planar spring strips 321,323. Theflexible strips 321,323 twist back and forth about the axis A causingthe member 303 to vibrate, and the mirror 359 reciprocates in bothcircumferential directions through an arc about the axis A.

When the laser diode emits a light beam, this light beam travels alongpath portion 100 and impinges on the scan mirror 212 and, in turn, isreflected along path portion 102 to the reflector 359 which, in turn,reflects the light beam along path portion 104 toward a target surfaceon which an indicia appears. The beam emerges through an opening formedin a side of the module. The reciprocal vibration of the reflector 359,during emission of the beam from the laser diode, causes the beam toscan a line across the indicia.

If module 400 is horizontally mounted in a scanner the resultant scanline would be horizontal and would scan an indicia having vertical bars.In contrast, if the module 400 is mounted vertically in a scanner, theresultant scan line would be vertical and would scan an indicia havinghorizontal bars.

The light reflected back by the indicia passes back along path portion104, whereupon it is reflected along path portion 102 for collection bythe concave collection mirror 204. The collection mirror 204, in turn,reflects the returned light along path portion 106 through the ambientlight blocking optical filter 210 for application to the detector. Thefilter blocks most light wavelengths but passes light of a wavelengthcorresponding to the wavelength of the light beam emitted by the laserdiode. A louvre can also be placed in front of the detector.

The detector 206 produces an analog proportional to the intensity of thereflected light which is processed, digitized and may be decoded by theapplication specific integrated circuit 419. Electrical leads forcarrying signals from the detector to the application specificintegrated circuit 419 are not illustrated for clarity.

The small size of the flexible support structure 300 provided in thescanning module does not prevent operation at low scanning frequencies.Again, the location of the reflector and magnet at opposite ends of themember 303 positions the weight thereof relatively far from the pivotaxis, thereby providing a high moment of inertia. Also, the mass of themoving components is fairly large; and the preferred materials of thesprings 321,323 tend to be quite flexible. The high mass, high inertiaand spring flexibility, cause the flexible support structure to exhibita relatively low characteristic frequency of vibration. Thus, the smallself-contained scanning module 400 operates at the low scanningfrequencies preferred for bar code scanning, such as 20 Hz or less.Also, the module 400 incorporates the balancing of the weight of thereflector and the weight of the permanent magnet which reduces oreliminates undesirable vibrations which might disrupt the scanningmotion and minimizes the amount of power which must be applied toinitiate motion of the scanning component, making the scanner moreefficient.

Although the embodiment discussed above is presented with reference to asingle laser arrangement it will be appreciated that more than one lasercan be incorporated into the module as appropriate (for example wholedual range scanning as discussed in more detail below). The lasers couldbe of any known type, for example conventional lasers, laser diodes or acombination thereof. Such an arrangement is shown in FIG. 7b in additionto the scanning assembly shown generally at 300 in this figure, a farlaser for scanning more distant items shown at 310 a and a near laserfor scanning closer items is shown at 310 b. The far laser beam isdirected by a fold mirror 310 c onto the common mirror 359 with the nearlaser beam.

Referring to FIG. 1b one possible implementation of the scanning module400 shown in FIGS. 2 to 6 or FIG. 7 (discussed in more detail below) isshown. As can be seen the module 400 is simply located and positionedwithin a gun-shape type reader 10. Where appropriate the same referencenumerals are used as have been used throughout the description. Themodule 400 can be secured by any suitable means and is aligned such thatthe outgoing beam 104 issues in the scanning direction through scanningwindow 56. One or other of circuit boards 416,418 can alternatively belocated in the pistol grip-type handle, or, as shown, an additional PCcard can be retained separately in the handle. The ease of manufacturingof such an arrangement will be evident as the self-contained scanningmodule is simply positioned and secured appropriately within thegun-type scanner 10. If the additional PC card 61 is installed then thiscan also be easily secured in the handle 53 and connected to the module400 in a conventional manner. The resulting device will have theadvantages of the gun-type scanner together with the reduced size andweight benefits provided by the module of the present invention.

The flexible support structure could be modified to provide beam spotscanning in two directions which are substantially orthogonal to eachother. A number of different scanning applications call for scanning intwo different directions. One such application provides a scan patternwhich moves across a bar code type indicia to find portions thereofwhich are sufficiently intact to permit an accurate reading of the code.Bi-directional scanning applications relate to scanning of indiciaencoded in two different dimensions.

A two-dimensional bar code comprises a series of rows or lines ofoptically encoded information. Each row is oriented in the X-direction(horizontal), and a plurality of rows is located one above another inthe Y-direction (vertical). Each row or line of information comprises aseries of encoded symbols, and each symbol consists of a series of lightand dark regions, typically in the form of rectangles. The widths of thedark regions, the bars, and/or the widths of the light spaces betweenthe bars indicate the encoded information on each row or line.Two-dimensional bar codes can carry considerably more encodedinformation than the common one-dimensional codes.

To read a two-dimensional indicia, it is desirable to scan the indiciawith a raster or similar type of scan pattern. In such a scan pattern, afairly large number of substantially horizontal and substantiallyparallel scan lines traverse the indicia from an upper horizontal scanline, proceeding downwardly with a multiplicity of intermediatehorizontal scan lines to a lower horizontal scan line to uniformly covera desired scan area encompassing the indicia. In order to obtain such araster-type scan pattern, the scanning component must be supported forreciprocal motion in two different directions. Also, the frequency ofoscillation in a first direction producing the X-direction spot scanningmotion typically is considerably higher than the frequency ofoscillation in a second direction producing the Y-direction spotscanning motion.

FIG. 7a depicts another embodiment of a module, and is analogous to theFIG. 2 embodiment, except in the following two respects. First, a radiofrequency transmitter 450 is mounted on the printed circuit board 418,and is coupled to a transmitting antenna 452 for broadcasting electricalsignals to a remote host device. The signals can either be the digitizedor the decoded signals generated by the scanner. The resultant “wirelessscan module” can be employed in a myriad of applications.

FIG. 7a also shows a second casing 412′ in which another laser diode ismounted, for emitting another light beam long a path portion 108 throughan aperture in the scan mirror 212 for impingement on the reflector 359.This “dual laser” module is useful for multiple line scanningapplications.

Although the present invention has been described with respect toreading one or two dimensional bar codes, it is not limited to suchembodiments, but may also be applicable to more complex indicia scanningapplications. It is conceivable that the method of the present inventionmay also find application for use with various machine vision or opticalcharacter recognition applications in which information is derived fromother types of indicia such as characters or from the surfacecharacteristics of the article being scanned.

In all of the various embodiments, the elements of the scanner may beassembled into a very compact package. Such a module can interchangeablybe used as the scan engine for a variety of different types of dataacquisition systems. For example, one or more modules may be alternatelyused in a hand-held scanner, a table top scanner attached to a flexiblearm or mount extending over the surface of the table or attached to theunderside of the table top, or mounted as a sub-component or subassemblyof a more sophisticated data acquisition system. A plurality of modulesmay be spatially positioned so that several overlapping reference planesor fields of view may be scanned or imaged. Control or data linesassociated with such components may be connected to an electricalconnector mounted on the edge or external surface of the module toenable the module to be electrically connected to a mating connectorassociated with other elements of a data acquisition system.

An individual module may have specific scanning or decodingcharacteristics associated with it, i.e., operability at a certainworking distance, or operability with a specific symbology or printingdensity. The characteristics may also be defined through the manualsetting of control switches associated with the module. The user mayalso adapt the data acquisition system to scan different types ofarticles or the system may be adapted for different applications byinterchanging modules on the data acquisition system through the use ofthe simple electrical connector.

The scanning module described above may also be implemented within aself-contained data acquisition system including one or more suchcomponents as a keyboard, display, printer, data storage, applicationsoftware, and data bases. Such a system may also include acommunications interface to permit the data acquisition system tocommunicate with other components of a local area network or with thetelephone exchange network, either through a modem or an ISDN interface,or by infrared or low power radio broadcast from the portable terminalto a stationary receiver.

Referring now to FIG. 8 there is shown an alternative configuration fora scanning module generally designated 500. The module includes a laser510 for generating a scanning beam 511 which passes through a lenssystem generally designated as 512. As in the previous embodiments, thescanning beam 511 is incident on a mirror 520 which is arranged tooscillate about a pivot point 521 to scan the beam as shown generally byarrows 513 and 514. The assembly is mounted on a circuit board 501 whichincludes an interconnect for a wall-forming circuit board (as discussedin relation to the previous embodiments) 502. As discussed above afurther circuit board (not shown) is mounted parallel to the basecircuit board 501. The means for mounting the module 500 are provided at503 and 504. A receiving photodiode and suitable information processingmeans such as a filter and a louvre are provided at 516, 517 and 518respectively. Those components receive and process the returning lightbeam in a manner generally known and discussed in relation to typicallythe size of the base board 501, relating to the dimensions A and B mightbe A=0.7″ (17.8 mm) and B=0.75″ (19.1 mm). The typical height might bein the region of 0.42″ (10.67 mm).

The arrangement shown in FIG. 8 is particularly appropriate forminiature scan elements having, for example, the dimensions discussedabove. In previous modules it has been noted that pointing errors arisein such miniature modules as a result of the difficulty of obtainingmass balance, which also gives rise to the problem of droop. This isparticularly a problem when it is desired to achieve the low frequencyscanning discussed above. The present invention overcomes thedifficulties by using the particular mirror configuration shown. Lookingat the configuration in more detail the mirror 520 is mounted on, or ona common body with a permanent magnet 521. The mirror system comprisingthe mirror 520 and the permanent magnet 520 pivot relative to a fixedpoint 523 on the base board 501 via a pivot shaft 522. The mirror systemextends from one side of a pivot shaft 522 perpendicular to the pivotaxis and the mirror 520 and permanent magnet 521 face in opposingdirections relative to a nominal line extending perpendicular to thepivot shaft 522. The mirror system is driven for scanning motion by acoil 524 which produces an alternating magnetic field in a mannerdiscussed with reference to the embodiments of FIGS. 2 to 6. Thealternating magnetic field drives the permanent magnet 521 back andforth giving rise to the scanning motion. This configuration differsslightly from that discussed with reference to FIGS. 2 to 6 in that themirror 520 and permanent magnet 521 are disposed both on the same sideof the pivot shaft 522 rather than on opposing sides thereof.

In view of the miniaturisation of the system it is difficult to providesufficient mass on the mirror system to increase the moment of inertiaand hence reduce the frequency of oscillation by a sufficient amount.Even the mass that can be introduced tends to give rise to droop and theaddition of any further mass would enhance that problem. This isovercome in the embodiment shown in FIG. 8 by introducing an additionalmagnetic element 530 positioned on the base board 501 in the vicinity ofthe permanent magnet 521. The element 530 can, for example, be an ironbar projecting from the base board 501. Because of the magneticinteraction between the iron bar 530 and the permanent magnet 521 thepermanent magnet 521 and hence the mirror system as a whole are biasedinto alignment with the iron bar. An effective increase of the mass ofthe mirror system is thus achieved and pointing errors/droop areaccordingly reduced. It will be appreciated, of course, that the ironbar can be replaced by any other suitable magnetic element 530.

According to another aspect of the invention there is provided a scannermodule system adapted to overcome the difficulties associated withinterference caused by ambient light in scanner environments.

This problem is particularly encountered with non-retro-collective barcode scanner systems in which the detector does not collect only thereading beam generated by the scanner, but also ambient light. Thisgives rise to inferior performance, especially in medium to high ambientlight conditions. As will be appreciated the problem can be addressed byproviding appropriate filters for the reflected light to filter outnoise resulting from ambient light conditions. The spatial filtering ofthe noise is dictated by the scan pattern produced by the light receivedfrom the reflected bar code. The temporal filtering of the noise isdictated by the wave form produced by the light received from thereflected bar code. Typically the spectral filtering is determined bythe following factors:

a) wavelength variation due to visible laser diode (VLD) manufacturingvariability;

b) wavelength variation due to VLD aging;

c) wavelength variation with temperature for a given VLD;

d) dependence of optical transmission on the angle of the receivedlight;

e) multiple mode lasing of VLD.

In order to accommodate all of the above factors, typically filters havea bandwidth of approximately 70 nm. This is orders of magnitude widerthan the spectral width of a single VLD mode and, as a result, a largeproportion of unnecessary noise caused by the ambient light conditionsis retained. Furthermore the filtering parameters cannot be changedwithout an impact on the scanner performance.

Referring to FIG. 9 one solution presented by the present invention isshown. The arrangement includes a fixed filter and a VLD having tuneablewavelength, the tuning parameter being the temperature of the VLD.

A scanner module is shown generally at 540. It will be appreciated thatthe components discussed below may be included on a single module of thetype discussed with reference to the embodiments above or in any otherappropriate form. The module 540 includes a laser 541 emitting a readingbeam 542. The beam 542 is redirected by a reflector 543 onto a scanningsystem 544 represented in the figure by a single reflector which isremovable to scan the beam 542 by reciprocating in a directionrepresented by arrow A. The resulting scanning beam is figurativelyshown by main beam 555, the scanning limits being shown by broken lines556,556′. In order to tune the wavelength of the laser 541 usingtemperature as the tuning parameter, the laser 541, which can bepackaged on a sub-mount or in a chip form in any known manner is placedon a thermo-electric cooler/heater unit 560. The cooler/heater unit 560can be of any known type, for example of the type where the temperaturecan be changed by varying the magnitude and direction of current flowingthrough it. As a result the wavelength of the laser 541 can bemaintained within the pass band of the filter for the detector (notshown) and a narrower pass band can thus be used.

The temperature can be controlled in various ways, generally relying ona feed-back signal. For example reflector 543 can be partially silveredso as to reflect the majority of reading beam 542 but transmit a portionof the reading beam as shown at 561. The transmitted beam 561 isreceived by an auxiliary detector 562. The auxiliary detector 562 may beprovided on the module 540, or maintained in the scanner housing asappropriate. The auxiliary detector 562 monitors the wavelength of thetransmitted portion of the reading beam 561 and provides a controlsignal to the cooler/heater unit 560 such that a desired temperature isattained to maintain the wavelength of the reading beam 542 within thepass band of the filter. The control signals are passed via a controlline 563. One way of controlling the temperature in this way is to tunethe auxiliary detector 562 to provide maximum response at a desiredwavelength within the pass band. The cooler/heater unit 560 temperatureis controlled to maximise the output of the auxiliary detector 562.

This arrangement allows the wavelength of the reading beam 562 to bemaintained within a desired band. As a result the filter can have agreatly reduced band width as the wavelength drift can be closelycontrolled. Accordingly the majority of the extraneous noise caused byambient light conditions can be filtered out giving rise to improvedsignal to noise ratio and performance.

The embodiment shown in FIG. 9 is particularly well adapted tocountering the wavelength variation occurring because of factors a) toc) above, namely manufacturing variability, aging the temperature aswill be apparent. It will be appreciated that that embodiment will thusgive rise to improved performance.

The performance can be further enhanced using the embodiment shown inFIG. 10 which additionally takes into account wavelength variation owingto dependence of the optical transmission on the angle of the receivedlight. This is achieved by relocating the auxiliary detector such thatit lies downstream of the scanning system 544. The redirecting reflector543 can accordingly be wholly silvered. Instead a further partiallysilvered mirror 565 is placed in the path of the beam reflected by thescanning system 544 and covering the whole scan range such that aportion of the beams within the limits represented by numerals 556 and556′ are reflected and have redirected by the reflector 565. A detector566 detects the redirected portion of the reading beam. The detector 566detects both the wavelength of the reading beam (in a manner analogousto detector 562 discussed with reference to FIG. 9) and also providesinstantaneous information as to the scan angle. This information is fedto a controller 567 (which may be any suitable processor) and thetemperature of the cooler/heater unit 560 is controlled accordingly. Ofcourse it will be appreciated that the controller 567 may be integralwith the detector 566 or may form part of the controller for the module542 as a whole. The wavelength of the laser 541 can accordingly becontrolled to correct for variations in optical transmission dependenton the angle of the received light. It will be appreciated that thecooler/heater unit 560 and laser temperature must be varied at a ratefast enough to follow the variations in the scan angle in order for thisembodiment to operate. This can be achieved of course for sufficientlyslow scan rates, and faster scan rates can be accommodated by minimisingthe thermal mass of the entire cooler/heater unit 560 and laser 541system.

The system can be yet further improved to take account of variationsarising as a result of factor e), the fact that some VLD's lase atseveral spectral modes, by selecting a suitable VLD that lases in asingle longitudinal mode. Various VLD's are known that would meet thisrequirement, for example most index-guided VLD's. It will be appreciatedthat even if the VLD lases in a few modes, improvements will berecognised although they will not be of significance.

In an alternative approach a VLD of fixed wavelength can be incorporatedand a tuneable filter can instead by used. In that case the controlsignals received from the auxiliary detector 562, or combined wavelengthand scan angle detector 566 would be fed to the filter such that thefilter followed variations in wavelength of the laser 541. Suitabletuneable filters are known, for example, from Optical Engineering Volume20, No. 6 (November/December 1981) pages 805 to 845 which comprises acollection of several articles on electronically tuneable opticalspectral filters. As will be appreciated the remaining features of thesystem would be similar to those described with reference to FIGS. 9 and

According to a further aspect of the invention it is desired to improvethe reading of poor quality one-dimensional bar code symbols. It isknown to enhance accuracy when reading one-dimensional bar code symbolsby using a reading beam having an elliptical cross section, the longaxis lying parallel with the bar direction or space direction, as shownin FIG. 11. The reading beam spot is shown exaggerated at 570 and scansas shown by arrow B along a bar code symbol 571. The reading beam spot570 is elliptical having its long axis parallel to the direction of thebars and perpendicular to the scan direction. As a result an averagingof the code defects in the vertical direction is provided.

It is desirable to increase the working range of a given scanner inorder that the scanner is more versatile. In order to increase thescanner working range for high density bar codes (6 to 10 mil), the farend of the working range can be increased by increasing the laserfocusing aperture size in the scanning direction, whilst the near end ofthe working range can be decreased by bringing the beam waist closer tothe aperture. This is shown figuratively in FIG. 12. A laser 575 emits abeam 576 through a circular focusing aperture 577. The beam 576 has awaist shown exaggerated at W. By increasing the aperture size in thescanning direction (shown again by arrow B) the working range increasesbut the beam waist decreases. As a result, if a badly printed bar codesymbol is scanned close to the laser beam waist, the reading beam spotwill be increased in size as a result of which there will be lessaveraging out of imperfections in a bar code symbol in the scanningdirection, causing noise in the read-out signal which cannot be filteredout by using an elliptical spot elongated perpendicular to the scanline. It is desirable to remove or reduce this performance degradationwhich will have an adverse effect on the working range.

The present invention solves the difficulties with the knownarrangements by identifying a parameter of the system that can be variedto improve conditions, namely the laser focusing aperture shape.Particular preferred shapes are described hereafter. It is found that ifthe focusing aperture shape is optimised, the laser beam waist can beincreased and a correspondingly improved signal to noise ratio obtainedfor poor quality bar code symbols without sacrificing the scannerworking range.

Conventional aperture shapes are generally circular or rectangular as aresult of which the only parameters available for increasing the scannerworking range are the aperture size and the beam waist location; thisgives rise to the decrease in the beam waist and the working range isincreased as discussed above. Various alternative aperture shapes areshown in FIGS. 13a to 13 c. Referring to FIG. 13a an optimised aperturehaving a stepped shape is shown. The aperture can be considered as beingformed by a series of rectangles A1, A2, A3, A1′, A2′, A3′ arrangedsymmetrically as shown. The rectangles of each pair A1, A1′ etc havesides of different length in the scan direction (shown once again byarrow B). The widest rectangles are found at the centre, the narrowestat the top and bottom.

In order to make the manufacturing process easier, and to decrease lightscattering at sharp corners, various alternative smooth shapes can beselected approximating the shape shown in FIG. 13a. For example as shownin FIG. 13b a rounded corner diamond shape could be used or in FIG. 13ca circular shape having upper and lower rounded lobes extendingtherefrom.

In fact the optimised aperture shape shown in FIG. 13a can be arrived atby MTF analysis, where MTF is the convolution integral for the aperturefunction. We now turn to mathematical treatment of the aperture shapeusing MTF analysis.

We assume that a scanner is intended to read 6, 7.5, 20 and 55 mil code.Typically, after optimisation of scanner working ranges, MTF for thehighest code density (6 mil in our example) changes vs. target distanceas illustrated by the cross-marked curve in FIG. 14. Let us assume thata digitizer can provide a reading at MTF>15%. In the shown example, ascanner having rectangular aperture of 0.027″ (0.686 mm) width, wouldprovided the working range from 2.5″ (63.5 mm) to 9″ (228.6 mm) for the6 mil bar code.

The MTF curve for the 6 mil code reaches a maximum value of about 45% atthe beam waist location at 5″ (130 mm) from the scanner. Nothing isadded to the scanner performance by having maximum MFT significantlyhigher than the threshold value of 15%. Instead, the scanner resolveshigher spatial frequencies representing the printing defects, and anoise level increases the beam around the beam waist location. Ideally,a flat MTF curve just above the threshold level is desirable. In otherwords, the beam waist can be increased until the flat MTF curve isreached.

Accordingly the additional degree of freedom in order to control theshape of the MTF curve is employed, namely the aperture shape whenreading one-dimensional bar codes. For the aperture shown in FIG. 13aconsisting of three rectangular areas with different sides along thescan direction x1, x2, and x3, taking into account, that MFT is theconvolution integral for the aperture function, one can calculate theMFT of the shown aperture by the following formula:

MTF=(MTF1.S1+MFT2.S2+MTF3+. . . )/(P1+P2+P3 . . . )

where MTFi is the MTF of i-th zone of the aperture, Pi is the laser beampower within the i-th zone. Therefore, we have an additional designfreedom by shaping the aperture. An example of the aperture, providingthe flat MTF for the 6 mil code is in FIG. 13a. Calculated MTF for the7.5 mils, 20 mil and 55 mil codes respectively are shown by the solidlines in FIGS. 15 to 17. One can expect that all printing defects withsize less than 6 mil will be filtered out.

Another possibility of the aperture shape optimization is to increaseworking ranges for the low density bar codes (40, 55 mil) when keepingwide ranges for high density bar codes as one can see from FIGS. 16 and17.

Referring to FIG. 14, the nominal MTF curve function for the “diamond”aperture and a 6 mil code is given by:${{MTF1}\left( {{wb},Z,x,{Ox},{Ax}} \right)} = \frac{\begin{matrix}{{{MTF}\left( {{wb},Z,x,{ex},{{Ax} + 0.011}} \right)} +} \\{{{MTF}\left( {{wb},Z,x,{ex},{Ax}} \right)} + {{MTF}\left( {{wb},Z,x,{ex},{{Ax} - 0.011}} \right)}}\end{matrix}}{3}$

Where wb is the code density, Z is the distance from the aperture (mm),x is the distance between the laser and the lens focal plane (μm), e isthe laser divergence angle and Ax is the aperture size of the relevantportion of the aperture (inches). The numerical values given correspondto the embodiment of FIG. 13a.

The distance WR is the working range as defined hereabove, and the MTFcurves are shown for a rectangular aperture (curve marked with crosses)and an optimized aperture (solid line). The threshold value of MTF=15%is shown with a dotted line, defining the working range WR.

FIGS. 15 to 17 use the same convention but for codes of 7.5 mil, 20 miland 55 mil respectively. The improvement in working range is representedby ΔWR. With respect to FIG. 17 a threshold value of 20% is selectedwhich is achievable, as discussed above, for such low density bar codes.

According to another aspect of the invention the problem of dead zonereduction for small scan modules is addressed.

Referring to FIG. 19 a conventional design for improving the performanceof small non-retro collective (one-dimensional and two-dimensional) scanmodules is shown from above. A pair of lenses 600,601 are associatedwith respective detectors (for example photodiodes) 602,603 in a scannermodule 605 of any type, for example the module type described above withreference to other embodiments of the invention. Other components of thescanner module 605 such as a laser etc. are not shown. The lenses serveto reduce the field of view and hence remove a portion of the backgroundnoise and ambient light. The lenses 600,601 also amplify the signalcollection area of the respective detectors 602,603 thereby increasingthe signal to noise ratio. The signals from both detectors 602,603 aresummed in a summing means of conventional type (not shown). Where thefield of view of each detector is shown as a respective opposing hatchedregion 604 and 605 respectively it will be seen that there is a regionof non-overlap referred to as the “dead zone” represented by distanceL_(d). It will be appreciated that within this region a non-uniformsignal will result when attempting to scan a printed indicia within thiszone. In particular the centre of the summed signal will either be nullor twice the amplitude of its ends. The dead zone defines a no-decoderegion as a result of which decoding near the “nose” or output window ofthe physical scan module is not achievable. It will be appreciated thatsuch decoding is often desirable, but if the photodiodes are moved backin order to have the field of view cover the “dead zone” working rangeis lost. A side view and front view of the arrangement of FIG. 19 areshown in FIGS. 20 and 21 respectively.

The solution proposed by the present invention is shown in the plan viewof FIG. 22. In addition to the two detectors 602,603 a third photodiodedetector 606 is located centrally in the module 605. The field of theview of the third detector 606 shown in dotted lines and represented byreference numeral 607. It will be seen that the third detector 606 willdetect signals within the dead zone, providing additional working rangewithout sacrificing the working range of principal detectors 602,603.Because the signal closer to the scanner module 605 is of relativelygood quality and much larger than it is further out, a small photodiodedetector will suffice. A smaller photodiode detector need not decodebeyond the distance L_(d) since the two larger detectors cover that areasufficiently. The smaller detector 606 is particularly of assistance indecoding near end indicia on the axis. In order for the pattern toappear suitably large, the laser path can be folded using a suitablesystem of mirrors. This can mean that the two principal detectors602,603 have to be moved further apart, but once again the thirddetector 605 alleviates the situation by covering the dead zone. A sideview and a front view of the arrangement according to the presentinvention is shown at FIGS. 23 and 24 respectively.

According to a yet further aspect of the invention it is desired toobtain multi-bit performance with minimal or no modification of existingcomponents. Various non-multi-bit scan modules are well known. Thiscomponent is incorporated with a scanning module or engine of the typediscussed with reference to FIGS. 1 to 7 above and in particularincludes a scanning signal input, a scanning signal digitizer and adigitized signal output together with an analogue signal differentiatorand output. It has previously been thought non viable to introduce amulti-bit version of such components as, unless an application specificintegrated circuit (ASIC) were introduced there would be no room on thesmall circuit boards provided in conventional scanning modules for theadditional multi-bit circuitry. In addition, multi-bit scan modules,even were they achievable, would be incompatible with decoders in allexisting portable terminals.

The present invention overcomes these problems by maintaining thecurrent scanning modules but making use of the existing components insuch modules to interface with a multi-bit decoder in an improvedmanner.

An example of the invention is shown in FIG. 25. A scanning module ofthe type described with reference to FIG. 2 (although any appropriatemodule can be used) is shown at 620. Only those components relative tothe signal processing are shown. The module 620 includes a signal input621 and a digitizer 622 arranged to convert the analogue input signal toa digital output 623. The digital output is held at an interface pin624. This allows the scanning module to be used in true modular form,arranged to interface with a suitable decoder module. In addition to thedigitizer 622 an analogue signal differentiator 625 is also provided.The output differentiated signal 626 is held at a second interface pin627. Conventional non-multi-bit systems have not made use of the secondinterface pin.

Referring to FIG. 26 a decoder module 630 is shown. For a non-multi-bitdecoding the digitized signal 623 is received from interface pin 624 anddecoded in decoder 631. The differentiated signal 626 interface pin 627is not used; the decoder uses the standard digitizer bar pattern signalprovided by the digitizer 622 on the scan board 620.

Multi-bit performance can be achieved with an appropriate decoder byusing the differentiator signal 626 in conjunction with the digitizedbar pattern signal from the digitizer 622. An analogue to digitalconvertor 632 is included as part of the decoder module 630. When thedecoder 631 detects a transition of the digitizer output from the scanengine it sends a signal via line 633 to a controller 634 causing theanalogue to digital convertor 632 to sample the differentiated signal.The analogue to digital convertor 632 therefore provides edge strengthinformation to the decoder 631 via lines 635. The scanning moduledigitizer 622 supplies edge location and polarity information. The mainprinciples of multi-bit signal processing are well known in the art andwill not be explored in detail here, but it will be seen that theparameters of interest can thus be monitored.

The analogue to digital convertor 632 can either be a separateintegrated circuit on a decoder board (as shown in FIG. 26) or can beincluded in the decode microprocessor chip itself. A suitablemicroprocessor chip is produced by Toshiba.

In cases where there are two positive or negative edges in a row in theinput signal 621, the conventional digitizer is very sensitive such thateven for a very small negative peak between two positive peaks or viceversa the digitizer 622 will detect all of the edges and the weaker oneswill be rejected using strength data in a conventional manner. It isbeen found that this does not lead to any significant cause ofdegradation of the signal processing.

FIG. 18 shows schematically the connection between the scan module 620and the decoder module 630.

It will be seen that the improved multi-bit modular arrangement can beincorporated with the design discussed with reference to FIGS. 1-7allowing yet further improvement in the interchangeability andmodularity of the arrangement, and a yet wider range of applications forthe basic retroreflective scan module described therein.

According to another aspect of the invention it is desired toincorporate dual or multiple lasers, and in particular dual-diodeperformance scanner functionality into increasingly small applicationsto meet the desired size/ergonomic considerations involved.

According to the invention, of which an embodiment is shown in FIG. 27,the dual-diode (ER) arrangement includes a first laser 700 focused forlong range scanning and a second laser 702 focused for short rangescanning. In order to obtain the small sizes requires the long rangelaser 700 is placed in a “back to back” configuration behind the shortrange laser 702. The long range laser beam 704 is folded around theshort range laser 702 by mirrors 706 and 708. The short range laser beam710 is folded by mirror 712. According to one embodiment the two beamsare recombined at 714 via a “special mirror” 716. The special mirror canbe partially silvered or slotted so as to reflect the short range beam710 but transmit the long range beam 704. Alternatively the specialmirror 716 could be off-set from the long range beam path 704 to allowthe long range beam 704 to pass the special mirror 716.

In addition to allowing reduced size, it will be seen that thisimplementation could be incorporated using existing modules, merelyincluding the additional components in the available space. Where amodular arrangement of the type discussed herein was used in will beseen that capability for adding additional lasers and components couldeasily be incorporated giving rise to greater adaptability andre-useability of existing components. It is certainly envisaged that thearrangement of FIG. 27 could be incorporated with the modulararrangement described with reference to FIGS. 1-6 above.

It will be understood that each of the features described above, or twoor more together, may find a useful application in other types ofscanners and bar code readers differing from the types described above.

While the invention has been illustrated and described as embodied in aretroreflective scan module for electro-optical readers, it is notintended to be limited to the details shown, since various modificationsand structural changes may be made without departing in any way from thespirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint or prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims. What is claimed as new and desired to be protected byLetters Patent is set forth in the appended claims.

What is claimed is:
 1. A wireless communications module, comprising: a)a support having a base lying in a first plane; b) a data acquisitionsystem including a light source on the base for directing a light beamat an indicium for reflection therefrom, and a light detector on thesupport for detecting light reflected from the indicium and forgenerating an electrical signal corresponding to the indicium; c) afirst printed circuit board on the support and lying in a second planegenerally orthogonal to the first plane; d) drive circuitry on the firstprinted circuit board for driving the light source; e) a second printedcircuit board on the support and lying in a third plane generallyorthogonal to the second plane and generally parallel to the firstplane; f) signal processing circuitry on the second printed circuitboard for processing the electrical signal to obtain a processed signal;and g) transmitter circuitry on the second printed circuit board fortransmitting the processed signal at radio frequency away from thesupport.
 2. The module of claim 1, wherein the transmitter circuitryincludes an antenna for transmitting the processed signal to a remotehost device.
 3. The module of claim 1, wherein the processed signal is adigital signal.
 4. The module of claim 1, wherein the transmittercircuitry includes a low power transmitter for transmitting the processsignal to a local area network.
 5. The module of claim 1, wherein thetransmitter circuitry includes a low power transmitter for transmittingthe processed signal to a telephone exchange network.
 6. The module ofclaim 1, wherein the transmitter circuitry includes a low powertransmitter for transmitting the processed signal to a stationaryreceiver.
 7. The module of claim 1, wherein the data acquisition systemincludes a scanner for scanning at least one of the light beam and afield of view of the light detector.
 8. The module of claim 7, whereinthe scanner includes a reflecting scan mirror mounted on the support foroscillating movement, and drive means for oscillating the scan mirror.9. A mobile data collection terminal, comprising: A) a housing supportedby a user; and B) a wireless communications module in the housing,including a) a support having a base lying in a first plane; b) a dataacquisition system including a light source on the base for directing alight beam at an indicium for reflection therefrom, and a light detectoron the support for detecting light reflected from the indicium and forgenerating an electrical signal corresponding to the indicium; c) afirst printed circuit board on the support and lying in a second planegenerally orthogonal to the first plane; d) drive circuitry on the firstprinted circuit board for driving the light source; e) a second printedcircuit board on the support and lying in a third plane generallyorthogonal to the second plane and generally parallel to the firstplane; f) signal processing circuitry on the second printed circuitboard for processing the electrical signal to obtain a processed signal;and g) transmitter circuitry on the second printed circuit board fortransmitting the processed signal at radio frequency away from thesupport.
 10. The terminal of claim 9, wherein the transmitter circuitryincludes an antenna for transmitting the processed signal to a remotehost device.
 11. The terminal of claim 9, wherein the processed signalis a digital signal.
 12. The terminal of claim 9, wherein thetransmitter circuitry includes a low power transmitter for transmittingthe processed signal to a local area network.
 13. The terminal of claim9, wherein the transmitter circuitry includes a low power transmitterfor transmitting the processed signal to a telephone exchange network.14. The terminal of claim 9, wherein the transmitter circuitry includesa low power transmitter for transmitting the processed signal to astationary receiver.
 15. The terminal of claim 9, wherein the dataacquisition system includes a scanner for scanning at least one of thelight beam of a field of view of the light detector.
 16. The terminal ofclaim 15, wherein the scanner includes a reflecting scan mirror mountedon the support for oscillating movements, and drive means foroscillating the scan mirror.